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Question
A person needs a lens of power –4.5 D for correction of her vision.
- What kind of defect in vision is she suffering from?
- What is the focal length of the corrective lens?
- What is the nature of the corrective lens?
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Solution
- The negative power of the lens suggests that she must be suffering from myopia.
- Power, P = ─4.5 D, focal length, f = ?
Now, P = 1/ f
⟹ f = 1/ P = 1/ −4.5 = −0.222 m = − 22.2 cm - Myopia is corrected using a concave or divergent lens.
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